Interesting Peculiarity (another Anomaly?)

Run the following:

declare @s1 varchar(10), @s2 varchar(10)
declare @t table(
recordid int identity(1,1)not null,
field char(1)not null)

insert @t (field) select 'a' union select 'b'
select @s1 = '', @s2 = ''
select @s1 = @s1 + field +',' from @t order by 1
select @s2 = @s2 + field +','from @t order by recordid
select
[Weird]=substring(@s1, 1,(datalength(@s1)-1)),
[Not]=substring(@s2, 1,(datalength(@s2)-1))